I have a bunch of PM 1.5 amps that I use (as intended) for pro-audio/sound reinforcement applications. Recently, I acquired several amps that have user-adjustments for the clip limiter on the faceplate--something I have not encountered before. All PM 1.5s have a switch to defeat/apply the limiter fuction (with which I am familiar), but these also have two RMS Output Voltage adjustments--one for a 1.5 second limit value variable from 45 to 77 volts, and one for a 30 second limit value variable from 20 to 77 volts. I purchased these from the original owner, and he has no idea regarding their purpose/function; however, they are secured by lock-nuts from the factory and are still set at the original factory specifications. I've done some preliminary research (still looking) and the original Carver Service Manual states that these controls were only present on the "first 1000 or so built."

It appears from the description below that these functions restrict the RMS voltage output both short and long term. Their settings would be a function of the drivers you were using on their outputs. For instance, voice coils can sustain short term RMS voltage higher than long term (and they cool off in-between).

Thanks for the input, hoping for some more. BillD, that's exactly what I know about these controls so far, but the user manual and service manual stop there. I'm hoping to find out what impact any adjustments would have on loudspeaker or amplifier protection. It appears (to me) that these are intended more to gate the amp's maximum output level, since the output of these amps is very dynamic.

Well, logic would have it that you set the short term voltage to what you voice coils can handle short term (1½ seconds) and the long term voltage (30 seconds) to what your voice coils can take longer term. With the top rail at 124V, a 100Vrms sine wave can be accommodated without clipping. That's a lot of pressure into a voice coil. Apparently, these adjustments will also shut your amp down when the values you set are exceeded for those threshold times, even if the amp isn't clipping.

If you want to try them out, get yourself some dummy loads. Calrods or toasters work fine.

Thanks--makes sense to me. Now I just have to dig up the specs for the drivers in these cabinets to see what they're up for (after some testing first). It would seem that you could take fuller advantage of the amp's dynamic power based upon the driver's ability to handle the higher output voltage. I use primarily Peavey and EV cabinets/drivers which can take quite a beating. Seems you could also do some serious damage downstream if you got "heavy handed". Probably why those controls were deleted after the first production run of 1000 units.